28 CYCADALBS [CH. 



prior to their further development in the lower chamber. Dr 

 Stopes^ regards the integument as double in origin, a view 

 suggested by Griffith^ in 1835, and as homologous with the single 

 integument plus the cupule of Lagenostoma. This view is supported 

 by Mrs Thoday* : on the other hand Miss Kershaw's investigation 

 of Bowenia seeds leads her to regard the integument as single. 

 Although there would seem to be a prima facie case in favour of 

 the dual nature of the integument, the arguments on the other 

 side have greater weight*- 



Eecent observations point to the probability that insects 

 play a part in the pollination of cycadean ovules. Kraus^ drew 

 attention to the strong smell emitted by the microstrobili of 

 Dioon edule and noticed that small bees were attracted to the 

 ripe strobili of Macrozamia, while odourless cones of a neighbouring 

 Ceratozamia received no attention. Pearson* and Rattray' have 

 obtained evidence that beetles and weevils act as pollinators to 

 species of Encephalartos. 



Anatomical features. Allusion has already been made to some 

 of the more striking anatomical features ; the large pith, the 

 occasional occurrence of medullary vascular bundles, the presence 

 of one or more cambiums, the large size of the medullary rays, 

 etc. It is worthy of remark that the occurrence of an anastomosing 

 system of medullary bundles is not a constant feature within a 

 genus; in Macrozamia Fraseri such a system is present, but 

 absent in M. Denisoni^. In the pith of stems with no medullary 

 bundles cylinders of collateral bundles may occur in connexion 

 with a fertile shoot. These bundles arise from the inner face of 

 the main cylinder and pass upwards as a domical system into 

 the base of the terminal strobilus which is eventually pushed to 

 one side by the growth of a lateral bud"- The secondary xylem 

 tracheids are usually provided with several rows of bordered 

 pits on the radial walls and resemble those of the Araucarieae", 

 but in Cycads the pits are often not contiguous and less compact 



1 Stopes (04). 2 OUver (13). 



^ Thoday (Sykes) (U); Sykes (10); Thoday (Sykes) and Berridge (12). 



* SaUsbury (14) p. 72. 6 Kraus (96). 



« Pearson (06). ' Rattray (13). 



' Worsdell (96); (01). » See ante, p. 5. 



" Chamberlain (11); Wieland (06). 



